minerals Article Carmeltazite, ZrAl2Ti4O11, a New Mineral Trapped in Corundum from Volcanic Rocks of Mt Carmel, Northern Israel William L. Griffin 1 , Sarah E. M. Gain 1,2 , Luca Bindi 3,* , Vered Toledo 4, Fernando Cámara 5 , Martin Saunders 2 and Suzanne Y. O’Reilly 1 1 ARC Centre of Excellence for Core to Crust Fluid Systems (CCFS) and GEMOC, Earth and Planetary Sciences, Macquarie University, Sydney 2109, Australia; bill.griffi[email protected] (W.L.G.); [email protected] (S.E.M.G.); [email protected] (S.Y.O.) 2 Centre for Microscopy, Characterisation and Analysis, The University of Western Australia, Perth 6009, Australia; [email protected] 3 Dipartimento di Scienze della Terra, Università degli Studi di Firenze, Via G. La Pira 4, I-50121 Firenze, Italy 4 Shefa Yamim (A.T.M.) Ltd., Netanya 4210602, Israel; [email protected] 5 Dipartimento di Scienze della Terra ‘A. Desio’, Università degli Studi di Milano, Via Luigi Mangiagalli 34, 20133 Milano, Italy; [email protected] * Correspondence: luca.bindi@unifi.it; Tel.: +39-055-275-7532 Received: 26 November 2018; Accepted: 17 December 2018; Published: 19 December 2018 Abstract: The new mineral species carmeltazite, ideally ZrAl2Ti4O11, was discovered in pockets of trapped melt interstitial to, or included in, corundum xenocrysts from the Cretaceous Mt Carmel volcanics of northern Israel, associated with corundum, tistarite, anorthite, osbornite, an unnamed REE (Rare Earth Element) phase, in a Ca-Mg-Al-Si-O glass. In reflected light, carmeltazite is weakly to moderately bireflectant and weakly pleochroic from dark brown to dark green. Internal reflections are absent. Under crossed polars, the mineral is anisotropic, without characteristic rotation tints. Reflectance values for the four COM wavelengths (Rmin, Rmax (%) (λ in nm)) are: 21.8, 22.9 (471.1); 21.0, 21.6 (548.3), 19.9, 20.7 (586.6); and 18.5, 19.8 (652.3). Electron microprobe analysis (average of eight spot analyses) gave, on the basis of 11 oxygen atoms per formula unit and assuming all Ti and 3+ Sc as trivalent, the chemical formula (Ti 3.60Al1.89Zr1.04Mg0.24Si0.13Sc0.06Ca0.05Y0.02Hf0.01)S=7.04O11. The simplified formula is ZrAl2Ti4O11, which requires ZrO2 24.03, Al2O3 19.88, and Ti2O3 56.09, totaling 100.00 wt %. The main diffraction lines, corresponding to multiple hkl indices, are (d in Å (relative visual intensity)): 5.04 (65), 4.09 (60), 2.961 (100), 2.885 (40), and 2.047 (60). The crystal structure study revealed carmeltazite to be orthorhombic, space group Pnma, with unit-cell parameters a = 14.0951 (9), b = 5.8123 (4), c = 10.0848 (7) Å, V = 826.2 (1) Å3, and Z = 4. The crystal structure was refined to a final R1 = 0.0216 for 1165 observed reflections with Fo > 4σ(Fo). Carmeltazite exhibits a structural arrangement similar to that observed in a defective spinel structure. The name carmeltazite derives from Mt Carmel (“CARMEL”) and from the dominant metals present in the mineral, i.e., Titanium, Aluminum and Zirconium (“TAZ”). The mineral and its name have been approved by the IMA Commission on New Minerals, Nomenclature and Classification (2018-103). Keywords: carmeltazite; Mt Carmel; volcanic rocks; corundum; spinel-derivative structure; desilication; extreme reduction 1. Introduction During the study of the mineral assemblage of rock fragments recovered from volcanic tuffs and associated placer deposits in the drainage of the Kishon River, near Haifa (northern Israel), several Minerals 2018, 8, 601; doi:10.3390/min8120601 www.mdpi.com/journal/minerals Minerals 2018, 8, x 2 of 10 Minerals 2018, 8, 601 2 of 11 During the study of the mineral assemblage of rock fragments recovered from volcanic tuffs and associated placer deposits in the drainage of the Kishon River, near Haifa (northern Israel), several exotic phases have been identified identified as accessory accessory minerals minerals (e.g., (e.g., [1] [1] and and references references therein). therein). In In that that area, area, a series of small volcanoes produced mafic mafic to ultr ultramaficamafic pyroclastic rocks (vent breccias, tuffs) in upper Cretaceous time [2,3]. [2,3]. These rocks contain a wide variety of xenocrysts, including megacrysts of clinopyroxene, ilmenite, zirc zirconon and corundum. Among them, aggregates of corundum crystals (Carmel Sapphire TM)) are are common common in in pyroclastic pyroclastic ejecta ejecta and and in associated alluvial deposits. Many of these aggregates aggregates contain contain crystals crystals of of an an unid unidentifiedentified Zr-Al-Ti-bearing Zr-Al-Ti-bearing phase, phase, up up to to 80 80 μµmm in in length. length. Chemical analysis and X-ray single-crystal diffracti diffractionon studies allowed the characterization of the new new Zr-Al-Ti phase, with thethe simplifiedsimplified formulaformula ZrAlZrAl22Ti44O11.. This This new new mineral mineral wa wass named carmeltazite from Mt Carmel (“CARMEL”) and and from from the the metals metals pr presentesent in the mineral, i.e., Titanium, Aluminum and Zirconium (“TAZ”). The mineral and its name have been approved by the IMA Commission on New Minerals, Nomenclature and Classification, Classification, underunder the number 2018-103. The holotype holotype specimen of carmeltazitecarmeltazite is is deposited deposited in thein mineralogicalthe mineralogical collections collections of the Museoof the diMuseo Storia Naturale,di Storia UniversitNaturale,à Universitàdegli Studi degli di Firenze, Studi di Via Firenze, G. La Pira Via 4,G. Florence, La Pira 4, Italy, Florence, under Italy, catalogue under number catalogue 3293/I. number 3293/I. The mineralogical description of of carmeltazite, as as well well as as its crystal structure, are given in this paper. 2. Occurrence Occurrence of Carmeltazite The new mineral described here, carmeltazite, occurs occurs in in pockets pockets of of trapped trapped melt melt interstitial interstitial to, to, or included in, skeletal corundum crystals (Figures 11–3).–3). TheThe earliestearliest paragenesesparageneses consistconsist ofof tistaritetistarite ± ± (Ti2O33)) ± carmeltazitecarmeltazite ± Mg-AlMg-Al spinel spinel in ina matrix a matrix ofof Ca-Mg-Al-Si-O Ca-Mg-Al-Si-O glass. glass. Figure 1. ((TopTop)) SEM-BSESEM-BSE image image of of carmeltazite carmeltazite (in (in corundum); corundum); scale scale bar isbar 200 isµ 200m; andμm; ( Bottomand (Bottom) phase) phasemap of map the of region the region highlighted highlighted in the in top the imagetop imag withe with a red a red dashed dashed rectangle rectangle (scale (scale bar bar is is 50 50µ m).μm). The silicatesilicate melts melts (probably (probably basaltic) basaltic) parental parental to this assemblageto this assemblage had previously had beenpreviously progressively been progressivelydesilicated by desilicated the exsolution by the of immiscibleexsolution Fe-Tiof immiscible oxide melts Fe-Ti and oxide Fe-Ti-Zr-silicide melts and Fe-Ti-Zr-silicide melts (found also melts as (foundinclusions also in as carmeltazite; inclusions Figurein carmeltazite;2), and the crystallizationFigure 2), and of the moissanite crystallization and khamrabaevite of moissanite (TiC), and Minerals 2018, 8, 601 3 of 11 Minerals 2018, 8, x 3 of 10 atkhamrabaevitef O2 = DIW-6 (TiC), or less. at fO This2 = Δ processIW-6 or less. continued, This process producing contin progressivelyued, producing lower progressivelyf O2, witnessed lower 2+ especiallyfO2, witnessed by the especially appearance by the of Tiappearance-bearing phasesof Ti2+-bearing (osbornite, phases khamrabaevite, (osbornite, khamrabaevite, unnamed TiB2, andunnamed unnamed TiB2, TiO). and unnamed TiO). Figure 2.2. ((TopTop)) SEM-BSE SEM-BSE image image of of carmeltazite carmeltazite (in (in corundum); corundum); scale scale bar isbar 200 isµ 200m;and μm; (Bottom and (Bottom) phase) mapphase of map the of region the region highlighted highlighted in the in top the imagetop imag withe with a red a red dashed dashed rectangle rectangle (scale (scale bar bar is 50is 50µm). μm). 3. Mineral Description and Physical Properties 3. Mineral Description and Physical Properties Carmeltazite (Figure1) occurs as black crystals, up to 80 µm in length and a few µm thick. Carmeltazite (Figure 1) occurs as black crystals, up to 80 μm in length and a few μm thick. The The streak is reddish brown and the luster is metallic. The calculated density is 4.122 g·cm−3 based on streak is reddish brown and the luster is metallic. The calculated density is 4.122 g·cm−3 based on the the ideal formula and single-crystal data (see below). Density was not measured because of the small ideal formula and single-crystal data (see below). Density was not measured because of the small amount of available material. amount of available material. In plane-polarized incident light, carmeltazite is weakly to moderately bireflectant and weakly In plane-polarized incident light, carmeltazite is weakly to moderately bireflectant and weakly pleochroic from dark brown to dark green. Internal reflections are absent. Under crossed polars, pleochroic from dark brown to dark green. Internal reflections are absent. Under crossed polars, the the mineral is anisotropic, without characteristic rotation tints. mineral is anisotropic, without characteristic rotation tints. The reflectance was measured in air by means of a MPM-200 microphotometer (CRAIC The reflectance was measured in air by means of a MPM-200 microphotometer (CRAIC Technologies, San Dimas, CA, USA) equipped with a MSP-20 system processor on a Zeiss Axioplan Technologies, San Dimas, CA, USA) equipped with a MSP-20 system processor on a Zeiss Axioplan ore microscope (Zeiss, Oberkochen, Germany). Filament temperature was approximately 3350 K. ore microscope (Zeiss, Oberkochen, Germany). Filament temperature was approximately 3350 K. Readings were taken for specimen and standard (SiC) under the same focus conditions. The diameter Readings were taken for specimen and standard (SiC) under the same focus conditions. The diameter of the circular measuring area was 0.05 mm. Reflectance percentages in the form (Rmin, Rmax (%) (λ in of the circular measuring area was 0.05 mm.